1. Field of the Invention
The present invention relates to a high expansion foam fire-extinguishing system for use in various warehouses, hangars, plants where dangerous objects are handled, cabins, holds, etc., and more specifically, to a high expansion foam fire-extinguishing system which helps to prevent a reduction in foam expansion ratio.
2. Description of the Related Art
In a foam fire-extinguishing system, a foam solution (hereinafter also referred to simply as an “solution”) is discharged from an emission nozzle, and is caused to impinge upon a foam screen to absorb air to thereby generate foam, with which the source of a fire is covered, thereby effecting a fire-extinguishing by eliminating oxygen. Such a foam fire-extinguishing system is of two types: a low foaming fire-extinguishing system and a high foaming (high expansion foam) fire-extinguishing system.
The above-mentioned two fire-extinguishing systems differ in foam expansion ratio; for example, in a low foaming fire-extinguishing system, the foam expansion ratio (multiplication) is 20 or less, and the foam is discharged from a foam head or the like so as to cover the floor surface or the like; as the foam concentrate, a aqueous film forming foam concentrate or the like is used. The foam expansion ratio of a high expansion foam fire-extinguishing system is not less than 80 but less than 1000; the foam is discharged from a foaming apparatus or the like so as to fill up the space; as the foam concentrate, a synthetic surfactant foam fire extinguishing concentrate or the like is used. Here, the term foam expansion ratio refers to the ratio in volume of the foam solution used for foam generation to the foam generated.
In order to generate high expansion foam at a foam expansion ratio, for example, of 500 or more, it is necessary to take in a large amount of air from the upstream side of the foaming apparatus (emission nozzle); when thus taking in a large amount of air, it is general practice to suck in air from outdoors (hereinafter referred to as “outside air”).
However, in a system using outside air, in order to use air in the exterior, a duct is provided in the building, or a hole is formed in the partition wall to arrange a foam generator, resulting in a rather high cost, etc.
In order to solve the above-mentioned problem, there is used a high expansion foam fire-extinguishing system of a type in which the air in the area where the foam is discharged (hereinafter referred to as the “inside air”) is sucked in (e.g., see JP 06-165837 A).
In an inside air type high expansion foam fire-extinguishing system, the foam expansion ratio as designed may not be attained depending upon the amount and quality of smoke generated at the time of a fire; there are cases in which, when the foam expansion ratio as designed is, for example, 500, the actual foam expansion ratio is only 100. When the foam expansion ratio is thus reduced, it becomes impossible to completely cover the fire source with the foam, with the result that the fire cannot be effectively extinguished by eliminating oxygen. As stated below, the reduction in foam expansion ratio is mainly due to the smoke in the sucked-in air.